The invention relates to a process for manufacturing a rolled-up plain bearing bush having a bearing width that varies over the length of the circumference and having machined peripheral ends.
Plain bearing bushes of this type are known. Such bearing bushes are used, in particular, as connecting rod bearings in the small end of the connecting rod in combustion engines. The varying bushing width is intended to effect a weight savings as compared to the solidly pressed-in plain bearing bushing, but are also adapted to geometric constraints at the side.
Until now plain bearing bushings of this type have been rolled as cylindrical bushings out of a rectangular, ribbon-shaped section of a strip of the bearing material or compound bearing material. Then the bushing was brought to the desired shape by machining in equipment for width turning. To do this, a rotationally driveable cutting tool with an axis of rotation set at an angle to the bushing""s longitudinal axis is advanced in an automated machine for width turning on one side or on both sides, so that the machined peripheral ends or peripheral end sections are lying in one plane. In this way a bushing shape described in a side view as what is known as a trapezoid can be achieved. After the so-called turning to width, the outer and/or inner bevel of the bushing ends has to be formed in a very complicated manner in additional machining involving metal removal.
Instead of equipment for turning the bushing to width, a known finished rolled cylindrical plain bearing bushing can also be machined by means of a milling cutter in such a way that it has a varying bushing width over the length of the circumference. If there should be any doubt, this process is even more complicated.
With rolled-up plain bearing bushings, punching out a relatively short rectangular recess from the material ribbon prior to the rolling procedure was also known. As a result, a bushing with varying width over the length of the circumference is certainly created, but machining of the punched out peripheral end section is not performed (see, for example, catalogue from Jorg Vogelsang GmbH and Co. from 1990, Metal Forming, page 14, Bearing Bushings).
GB-A-1 597 9604 teaches the manufacture of bushings with varying bushing width over the length of the circumference in pairs or in batches by demarcating several strips immediately adjacent to each other in the transverse direction from a single roll of flat material to produce several bushings. First, longitudinal sections are formed from several bushings next to each other in the transverse direction, which are then transferred and rolled up in the transverse direction. Only then in the rolled-up state are the bushings separated. If machining of the peripheral ends is desired, this has to take place subsequently.
Starting from this, it is desirable to create a rolled-up plain bearing bushing with a bushing width varying over the length of the circumference, which can be manufactured more economically and which has more uniformly machined peripheral ends than known bushings.
The process according to the invention is characterized in that after being rolled up, the plain bearing bushing does not have to undergo any machining to its width involving cutting. It has accordingly a well defined, clean side profile which, because of its rotationally non-symmetrical geometry, could never be achieved by means of the known machining to its width through metal cutting and subsequent side machining. The person skilled in the art can recognize without any difficulty from the finished product under the invention that the varying bushing width over the length of the circumference was not produced by a machining process involving metal cutting.
The plain bearing bushing under the invention, which is manufactured from a previously formed ribbon-shaped section of strip, that is, a formed blank, has the advantage that the bushing can be produced in the rolling-bending tool being finished without subsequent machining to width.
An offset shape, specifically, a multiple offset shape for the bushing width, can be produced in a particularly advantageous way, without the need for any metal-cutting machining to width. This is understood in the mathematical sense to be a discontinuous course of the peripheral ends. But even a course of the peripheral ends which is curved in sections, i.e., one that is non-linear, can turn out to be advantageous. It was possible to produce a shape of this type previously only by machining using a milling cutter.
The invention further proves to be advantageous if the side sections of the ribbon-shaped section of strip forming the circular peripheral ends have a coined bevel at least in sections, specifically one that is not created by removing metal by machining, which is introduced while still in the planar state before the section of strip is rolled up.
According to the procedure under the invention, a ribbon-shaped continuous roll of flat material is fed in its longitudinal direction to a cutting device, in which the side shape forming the terminating circular peripheral ends is cut into the roll of flat material. What is created is a profile of varying width running in the longitudinal direction. Bevels are then created along the edges of the profiled roll of flat material, preferably by means of coining. Then the sections forming the individual bearing bushings are separated from the continuous roll of flat material. These strip sections are then rolled up into the bushing shape to form the finished free-falling bearing bushing.
Preferably after cutting the side shape and before separating and rolling up the sections of the strip, each of the longitudinal sides is given an edge, profile rolled, and, if necessary, chased. In the same way, preferably before rolling up the strip sections, an oil groove and/or lubricating holes can be coined or stamped. After the bushings are rolled up, only a ball-sizing calibration and an outside draw calibration need to be performed.